fix: an asleep browser Lane is not a stalled one on the admin page

laneRow.Stalled was Due > 0 && Checked == 0, which is exactly the shape
of the on-demand wake gate declining to start Chrome (ADR-0005): under
five due Series and none overdue by 15m, a browser Lane reads nothing on
purpose. kagane and novelfull each have one bookmarked Series, so that is
their state for most of every cycle and the page marked both "not
checking" — spending the one mark that means "go look" on the commonest
healthy state.

LaneState.Asleep is set at the wake gate, excluded from Stalled, kept out
of Attention, and rendered as "browser asleep". Verified in prod: those
Lanes wake on the age rule 15m past due (kagane and novelfull both polled
at 14:55Z for a 14:40Z due moment, novelfull picking up Chapter 4458).

backend/internal/latest/poller.go

@@ -263,7 +263,7 @@ func (p *Poller) runLanePass(ctx context.Context, name string, paced bool) time.
 		// browser): waking it for a single Poll would cost a challenge solve
 		// per request. The Lane still paces at the default gap, which is what
 		// the owner's page must show rather than a zero.
-		st.Gap = defaultGap
+		st.Gap, st.Asleep = defaultGap, true
 		return defaultGap
 	}
 	if s.Browser != nil {